The invention relates to a calibration method and related calibration apparatus for correcting errors generated in data converter system, and more particularly, to a method and apparatus for digitally correcting code errors due to capacitance mismatch of a capacitor array in data converter system.
In integrated circuit technology, as capacitors are fabricated more easily than resistors, capacitors are usually used as the precise components in an analog-to-digital converter (ADC) or a digital-to-analog converter (DAC), which is referred to as charge-redistribution technology. Usually, the linearity of the overall ADC or DAC is limited by the linearity of the capacitors. Therefore, an ADC or DAC with high resolution will often require some form of trimming or calibration to achieve the necessary linearity. This is due to inherent component-matching limitations. The accuracy of the A/D or D/A conversion utilizing charge-redistribution is mainly determined by the matching of the capacitors in the capacitor array. To achieve high resolution and accuracy, a certain calibration for the capacitor array is necessary.
A conventional self-calibration technique for a capacitor array is illustrated in FIG. 1. As can be seen from FIG. 1, a charge-compensation calibration capacitor Ccc and a calibration digital-to-analog converter (DAC) 101 are utilized for calibrating a capacitor array 120 through a comparator 130 and a control circuit 140. This scheme mainly uses the charge-compensation calibration capacitor Ccc for compensating mismatches among the capacitor array 120 during the normal operation of the capacitor array 120. For example, the charge-compensation calibration capacitor Ccc draws charge from or injects charge to the capacitor array 120 while the ADC is performing A/D conversion. This process needs additional calibration cycle. As a result, the calibration operation significantly affects the sampling rate of the ADC, and the conversion speed is sacrificed. Obviously, these are disadvantages of the conventional capacitor calibration technique for a capacitor array that need to be solved.